Occupational studies are conducted to identify and quantify chemical and other causes of cancer and to understand mechanisms of carcinogenesis. Etiologic investigations utilize sophisticated industrial hygiene methods to assess occupational exposures and biochemical components to elucidate mechanisms of carcinogenic action and individual susceptibility. Methodologic studies are designed to improve study techniques and to provide direction for future research. Major etiologic investigations focus on working populations exposed to benzene, other organic solvents, acrylonitrile, formaldehyde, diesel exhausts, combustion products, electromagnetic fields, pesticides, and silica. Findings linking cancer with occupational exposures included an excess of prostate cancer among firefighers; excesses of leukemia and cancers of the liver, breast and ovary among nurses; higher rates of renal cell cancer from exposure to organic solvents among women than men; association between exposure to formaldehyde exposure and pancreatic cancer; high mortality from accidents, leukemia and pancreatic cancer among aerial pesticide applicators; excesses of pancreatic cancer among workers in China exposed to metals and textile dusts; and an excess of nasopharyngeal cancer among workers exposed to formaldehyde. Ongoing projects to evaluate occupational exposures include case-control studies of bladder cancer in Spain and New England, lung cancer in Russia, renal cancer in Eastern Europe, and non-Hodgkin's lymphoma in the U.S. Cohort studies of occupational groups include miners with exposure to diesel exhausts, farmers with exposure to pesticides and other agricultural chemicals, women in many occupations in Shanghai, and industrial workers with exposure to benzene in China.